1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus, a method of adjusting a beam incident angle to a target object surface, and a charged particle beam writing method. More specifically, for example, the present invention relates to a method of adjusting an incident angle of an electron beam to the target object surface in an electron beam writing apparatus that irradiates electron beams onto the target object while performing a blanking operation.
2. Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 19 is a conceptual diagram for explaining operations of a variable shaped electron beam writing or “drawing” apparatus. As shown in the figure, the variable shaped electron beam writing apparatus operates as described below. A first aperture 410 has a quadrangular opening 411 for shaping an electron beam 330. A second aperture 420 has a variable-shape opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shape opening 421 of the second aperture 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., the x direction) during the writing. In other words, a quadrangular shape that can pass through both the opening 411 and the variable-shape opening 421 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture 410 and the variable-shape opening 421 of the second aperture 420 is referred to as a variable shaped beam (VSB) system.
For example, in a writing apparatus of the VSB system, one shot beam is formed by a blanking operation. Generally, the writing apparatus has a deflection function for deflecting a plurality of beams, at a subsequent stage of a blanking deflector, and emits a beam to the surface of a target object while deflecting the beam by the beam deflection function (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2000-251827).
Then, in order to increase the position accuracy of writing, it is necessary that the beam incident angle to the target object surface does not change even when a blanking voltage changes during a beam-on period. For example, in the case of not performing a beam deflection other than a blanking operation, it is desirable that a beam incident angle to the target object surface is always perpendicular even when a blanking voltage changes during a beam-on period. If the incident angle deviates from a perpendicular incidence, a positional deviation will occur at the beam irradiation position on the target object surface when defocusing occurs. To solve this problem, it is necessary to measure an incident angle (a landing angle) of a beam in the case of performing deflection of the beam by fine-tuning a blanking voltage of during a beam-on period. However, with respect to voltage used for a blanking operation, generally, binary values of voltage of during a beam-on period and a beam-off period are set in the amplifier that applies a voltage to a blanking deflector in order to secure a blanking speed (response) and voltage stability. For example, a voltage used for a blanking operation is configured by binary values, such as 0V and several V. Since a beam deflected by the voltage of during a beam-off period is blocked by the blanking aperture, it does not reach the target object surface. Therefore, the blanking voltage of during a beam-on period cannot be fine-tuned, and therefore it is difficult to measure a beam incident angle by using the voltage of an existing blanking operation.